The present invention relates to a double-headed piston type compressor for use in a vehicle air conditioning system.
A compressor disclosed in Japanese Patent Application Publication No. 2007-138925 discloses a suction mechanism including a rotary valve for introducing refrigerant into front compression chambers of the compressor and another suction mechanism including suction valves for introducing refrigerant into rear compression chambers of the compressor. A lip seal-type shaft seal is interposed between a front housing and a rotary shaft of the compressor. The shaft seal is accommodated in a shaft seal chamber formed in the front housing. A recessed passage is formed in the outer circumferential surface of the rotary shaft to serve as a part of the rotary valve. One end of the recessed passage is open to the shaft seal chamber having therein the shaft seal. The other end of the recessed passage is open to the suction passages which are formed in a front cylinder block of the compressor in communication with compression chambers. As the rotary shaft rotates, each suction passage intermittently communicates with the recessed passage, so that refrigerant in the shaft seal chamber is introduced into the compression chambers through the recessed passage and the suction passages.
Since the recessed passage is formed by machining a groove in the outer circumferential surface of the rotary shaft, the manufacturing cost of the rotary shaft is reduced as compared to forming a passage by boring the end of the rotary shaft. Further, the refrigerant flowing through the shaft seal chamber cools the shaft seal, which extends the life of the shaft seal.
However, the recessed passage of the rotary valve disclosed in the above reference No. 2007-138925 extends so as to connect the shaft seal chamber in the front of a valve port plate and the suction passages at rearward of the valve port plate. Thus, the outer circumferential surface of the rotary shaft needs to be grooved for a long distance in the axial direction of the rotary shaft to form the recessed passage. As the length of the recessed passage in the axial direction is increased, the strength of the rotary shaft is reduced. Further, there is another problem in that the shaft seal needs to be located further forward by a distance for which the recessed passage extends forward of the valve port plate. This causes the compressor to become large in size.
The present invention, which has been made in view of the above problems, is directed to providing a double-headed piston type compressor that prevents decreasing the strength of the rotary shaft while minimizing the size of the compressor.